In recent years, displays in image display devices, such as television devices, are being shifted from conventional cathode-ray tube displays to thin displays, such as liquid crystal displays and plasma displays. With the thin displays, thicknesses of the image display devices can be decreased. Liquid crystal panels do not emit light. Therefore, liquid crystal display devices including liquid crystal panels require backlight devices. An edge-light type backlight device is known as one example of the backlight device. The edge-light type backlight device includes a light guide plate with a light entrance surface on the side and light sources such as LEDs arranged closer to the side of the light guide plate.
In the edge-light type backlight device, the light guide plate may move in its plate surface direction due to vibrations of the light guide plate or a fall of the backlight device. This may change a distance between the light guide plate and the light source. If the distance between the light guide plate and the light source changes, an optical design may not remain preferable. For such a reason, in the edge-light type backlight device, it is required to provide a configuration that causes less or no movement of the light guide plate and keeps a constant distance between the light guide plate and the light source.
Patent document 1 discloses a backlight unit including a light guide plate held in a chassis. In Patent document 1, the light guide plate is less likely to move in its plate surface direction due to the vibrations thereof. In the backlight unit, ribs having spring properties are disposed between the light guide plate and side plates of the chassis to maintain the distance between the light guide plate and the chassis. In this configuration, the light guide plate is less likely to move in its plate surface direction because of an elastic force of the ribs.